William Bratton at a news conference in New York, Thursday. Bratton, whose tenure as New York City police commissioner in the 1990s was marked by a steep decline in crime, has been chosen to lead the nation's largest police force again. Mayor-elect Bill de Blasio announced the appointment Thursday, saying Bratton is a "proven crime-fighter" who knows how to keep the city safe.

In naming William Bratton to be New York police commissioner, Mayor-elect Bill de Blasio has chosen one of the nation’s best-known and most well-traveled law enforcement officials.

In addition to heading New York City’s police department once before – under former Mayor Rudolph Giuliani from 1994 to 1996 – Mr. Bratton has been police chief in Los Angeles and Boston. British Prime Minister David Cameron considered naming him Metropolitan Police Commissioner in London.

During his 43 years in law enforcement, Bratton rose quickly through the ranks, becoming chief of police in his native Boston at age 32. The NYPD is the largest law enforcement organization in the US, with a uniformed force of about 34,500 officers.

Any New York police commissioner faces major challenges: maintaining the trend of dropping crime rates in the city, avoiding corruption scandals, and keeping the city safe from terrorist attacks in a post-9/11 world.

“Together, we are going to preserve and deepen the historic gains we’ve made in public safety – gains Bill Bratton helped make possible,” Mr. de Blasio said in a statement. “And we will do it by rejecting the false choice between keeping New Yorkers safe and protecting their civil rights.”

There reference here is to the controversial “stop and frisk” program critics say illegally targeted black and Latino men.

A federal judge ruled over the summer that the NYPD sometimes carried out its stops unconstitutionally by unfairly targeting minorities. Her ruling is on hold pending an appeal by the city.

The appeal won't be heard until after de Blasio takes office, and he has said he'd drop it. De Blasio made reforming, but not eliminating, stop-and-frisk one of the centerpieces of this mayoral campaign.

Bratton has said he supports stop-and-frisk, but only if it is carried out fairly and not as part of racial profiling.

“Bill Bratton knows that when it comes to stop-and-frisk it has to be used with respect and it has to be used properly,” de Blasio said in announcing Bratton’s appointment at the Red Hook Community Justice Center in Brooklyn Thursday. “He is going to bring police and community back together.”

In a recent interview in the urban-affairs magazine City Journal, Bratton elaborated on his approach.

“I’ve spent my life in the police profession, and I’m proud of that,” he said. “But I am also very cognizant of the profession’s limitations, its potential for abuse, and its potential negative impact.”

“Policing has to be done compassionately and consistently,” Bratton continued. “You cannot police differently in Harlem than you’re policing downtown. The same laws must apply. The same procedures must be employed. Certain areas at certain times may have more significant crime and require more police presence, or more assertiveness, but it has to be balanced. If an African-American or a recent immigrant – or anyone else, for that matter – can’t feel secure walking into a police station or up to a police officer to report a crime, because of a fear that they’re not going to be treated well, then everything else that we promise is on a shaky foundation.”

In his work heading big-city police departments around the country, Bratton also emphasizes the importance of crime prevention. This includes the “broken-windows” theory of policing, which focuses on vandalism and other minor crimes as creating an atmosphere that leads to more major offenses in certain urban neighborhoods.

Bratton also helped spearhead the use of CompStat, a data-driven system of tracking crimes that allows police to better allocate their resources to high-crime areas. The real-time system is used by many police departments today.

During his earlier stint heading the NYPD, the crime rate in the city dropped, as it did when he went on to head the LAPD. The drop was 30 percent in Los Angeles.

"Los Angeles’ police force is better trained, more diverse, better disciplined and better led than the one that betrayed the city's trust in 1992," The Los Angeles Times declared when Bratton left after seven years on the job. "Its work is appreciated by residents across racial lines. Its record, though not perfect, is far less inflammatory and far more constructive."

De Blasio’s announcement Thursday was generally well-received.

“The mayor could not choose a better police commissioner than Bill Bratton,” Manhattan District Attorney Cyrus R. Vance Jr., told The New York Times. “He already has the respect of the men and women in the NYPD, and the public will be comforted to know that a tested and a seasoned veteran will again lead the nation’s finest police department and ensure both our safety as well as fairness in the justice system. It’s a great choice.”

Sgt. Ed Mullins, president of the 12,000-member Sergeants Benevolent Association had this to say about Bratton:

“Commissioner Bratton’s ingenuity and creativity was responsible for the tremendous turnaround that we’ve experienced in this great city over the past two decades…. Although he has very high expectations of those who work for him, morale in the Department was never greater than when he was the commissioner. He brings out the best in people, and all of the city’s residents, as well as Department members of every rank, will be well-served by his appointment.”